Static assert that field types are trivial

[bernhardmgruber]

LLAMA assumes in many places that the types used in fields are trivially constructible, copyable and destructible. This should be asserted on the types used in the record domain. If this property is not fulfulled, LLAMA should fail to compile to prevent unwanted results.

[bernhardmgruber]

For a LLAMA view itself, it suffices that the field types are trivially constructible and destructible.
Trivial copyability might be relevant for LLAMA's copy, but that is not yet inside the LLAMA library (it's in the viewcopy example).

But rather than forbidding copies of non-trivially-copyable types, we could actually just run their copy dtors.